Finland recently activated the world’s largest sand-based thermal battery in the small town of Pornainen, an innovative project that is turning heads due to its low cost and promising environmental impact.
Unlike conventional battery storage—which typically involves expensive materials like lithium-ion—this thermal system uses crushed soapstone, an inexpensive waste product from a Finnish fireplace manufacturer. The entire storage mechanism, containing approximately 2,000 metric tons of the pulverized stone, sits within a 49-foot-wide insulated silo. While the sand battery may not capture the eye like its high-tech counterparts, its economic appeal and eco-friendly credentials certainly do.
The technology operates by converting electricity—preferably sourced from renewable energy—into thermal energy, heating the soapstone to extremely high temperatures. This heat can then be stored efficiently for weeks, offering an effective method of seasonal energy storage. According to its creators, this thermal battery can store and deliver up to 1,000 megawatt-hours of heat at temperatures reaching 400 degrees Celsius, with heat losses limited to roughly 10-15%.
Pornainen, like many towns in Scandinavia, utilizes a district heating system, which traditionally relies on centrally heated water circulated to homes and commercial buildings. Currently powered by burning wood chips along with oil, the heating network stands to significantly reduce its environmental impact by shifting from fossil fuels to cleaner stored heat. Polar Night Energy, the developer of the thermal battery, projects that local dependency on wood chips will drop by around 60%, and that consumption of expensive oil can be virtually eliminated. Although the battery is primarily being used for heating, it has potential for electricity generation as well, albeit with slightly reduced efficiency.
Interest in thermal energy storage has surged recently, driven by the declining price of renewable energy sources. Similar ventures are cropping up globally. Companies such as Scotland’s Sunamp, Electrified Thermal Solutions, and Fourth Power in the U.S. are each developing distinct kinds of thermal storage systems. What differentiates these systems is the material chosen for storing heat—ranging from specialized chemical substances to durable bricks and graphite blocks—each capable of storing energy at extremely high temperatures.
The electricity used to charge the thermal battery in Pornainen comes primarily from Finland’s notably clean power grid, comprising approximately 43% renewable energy and 26% nuclear power. Not only is the electricity sustainable, but Finland also enjoys some of the lowest power prices in Europe, averaging below €0.08 per kilowatt-hour, less than half the EU’s average rate.
Though the exact cost of Polar Night Energy’s new large-scale installation was not specified, earlier prototypes indicated strong economic competitiveness. Previous estimates pegged the smaller installations’ cost at approximately $25 per kilowatt-hour of storage. Since raw materials are inexpensive and the structure relatively simple, the economics for large-scale implementations like Pornainen’s battery are expected to be even more attractive, substantially lower than lithium-ion battery systems, which typically run around $115 per kilowatt-hour.
This Finnish project demonstrates growing potential for thermal storage systems worldwide, bolstering the global push toward sustainable, reliable, and cost-effective energy solutions.
